Many of the species are superficially very similar, particularly among the fine-leaved species. In these, the position of sclerenchyma tissue, as seen in a cross section of the leaf blade, is an important aid to identification. The type of branching of the basal vegetative shoots (tillers) is also important. If the shoot breaks through the base of the subtending leaf sheath a loose tuft results (extravaginal branching), but if it grows up inside the leaf sheath a denser tuft results (intravaginal branching).

The fine-leaved species include a number of species aggregates. The aggregate name has been used in the main key, as this will be sufficient for most users. Within the aggregates individual taxa are recognized either at specific or infraspecific rank, but the differences between the taxa are slight and often overlapping.

This large genus is divided into subgenera, which are indicated in the key. Recent molecular work is indicating that the larger broad-leaved species are not closely related to the fine-leaved species.

Most of the species provide good grazing, and some are important constituents of fine lawns.

About 450 species:temperate regions throughout the world, extending into the tropics on mountain tops; 55 species (25 endemic) in China.